/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution{
public:
  vector<int> inorderTraversal(TreeNode *root){

    vector<int> ans;

    inorderDFS(root, ans);

    return ans;

  }

  void inorderDFS(TreeNode *root, vector<int> &ans){

    if(!root){
      return;
    }

    inorderDFS(root->left, ans);
    ans.push_back(root->val);
    inorderDFS(root->right, ans);

  }

};